Spin-stabilized artillery projectiles are gyroscopically stabilized, spinning rapidly about the projectile's longitudinal axis resulting from the action of the rifling during the launch sequence. In free flight after muzzle exit, aerodynamic forces act on the projectile body, producing a complex epicyclic motion of nutation and precession throughout the trajectory that may affect, and otherwise interfere with, a desired trajectory of the projectile.
As the range capability of artillery weapons and ammunition grows, accuracy and precision of delivery become increasingly important. Total delivery errors for standard, unguided 155 mm artillery projectiles, including all error sources, can exceed 300 meters at 30 km, while a point target size may be less than ten square meters. In such a case, the probability of hitting a specific point target at extended range will be low unless a large number of rounds are fired. A number of techniques have been proposed to provide some measure of control over the flight path of spin-stabilized projectiles, all aimed at enhancing the accuracy and precision of artillery fire sufficiently to improve the chance of impact at point targets at extended ranges with reduced expenditure of ammunition and without inflicting collateral damage on objects located in the vicinity of the desired target.
Many techniques for controlling the flight path of spin-stabilized projectiles require knowledge of the orientation of the projectile referenced to the earth-fixed coordinate system. There are a number of existing horizon sensors and techniques for sensing or otherwise measuring or determining the projectile's orientation, but it is generally beneficial to improve upon existing techniques.